For the purpose of controlling the uneven wear of the tire, there have hitherto been made various means in the design of tread groove, tread crown form, tread pattern or the like such as defense grooves, side grooves and the like. However, these means have a problem that the control of the uneven wear is insufficient. In general, non-uniform wear is caused in ribs, blocks and the like of the tire tread by various factors before the occurrence of the uneven wear in the tire.
Since such a non-uniform wear is caused by an input in a radial direction, an input in a circumferential direction or an input of a composite thereof with respect to a rotating direction of the tire, it is attempted to improve the resistance to uneven wear by using a rubber composition hardly affected by these inputs in a tread and combining with a tire structure.
In order to prevent the uneven wear in the tire, there is used a method of using a rubber composition compounded with styrene-butadiene copolymer rubber in the tread to enhance hysteresis loss. However, the compounding of the styrene-butadiene copolymer rubber deteriorates the heat buildup of the tire, so that there is particularly a restriction in the compounding amount thereof in heavy duty tires.
Now, there is proposed an attempt that a solution-polymerized styrene-butadiene rubber modified at a terminal of its polymer molecule is used to enhance dispersion of carbon black through a coupling effect of its modified terminal, whereby the self-heat generation is improved to make the heat buildup low to establish the resistance to uneven wear and the heat buildup (e.g. see JP-A-11-217004, page 3). However, it can not be said to be sufficient in the heavy duty tire.
Further, there is proposed a technique of establishing the resistance to uneven wear and the heat buildup by a combination of solution-polymerized styrene-butadiene copolymer rubber, silica and a silane coupling agent (e.g. see JP-A-11-59116, page 1).
However, silica has such an effect that the heat buildup is not lowered while enhancing the hysteresis loss, but has a fear of lowering the wear resistance under severe use condition in the heavy duty tire. In such a compounding technique, the resistance to uneven wear and the heat buildup are conflicting relation and it is difficult to establish them simultaneously.